1. Field of the Invention
The present invention relates to a heterocyclic compound represented by Formula 1, an organic light-emitting diode including the heterocyclic compound, and a flat display device including the organic light-emitting diode; and more particularly, to a heterocyclic compound that is suitable for use as a light-emitting material or electron transporting material included in an organic light-emitting diode, an organic light-emitting diode including the heterocyclic compound, and a flat display device including the organic light-emitting diode.
The heterocyclic compound has high glass transition temperature or high melting point, and thus, an organic light-emitting diode including an organic layer that includes the heterocyclic compound has a high charge transporting capability and a high light-emitting capability.
2. Description of the Related Art
Organic light emitting diodes are self-emission devices, and have a wide viewing angle, a high contrast ratio, a short response time, and high brightness, excellent driving voltage, and quick response speed characteristics, and enable generation of multi-color images.
In a typical organic light-emitting diode, an anode is formed on a substrate, and a hole transport layer, an emission layer, an electron transport layer, and a cathode are sequentially formed in this stated order on the anode. In this regard, the hole transport layer, the emission layer, and the electron transport layer are organic films including organic compounds. When a voltage is applied between the anode and the cathode, holes injected from the anode pass the hole transport layer and migrate toward the emission layer, and electrons injected from the cathode pass the electron transport layer and migrate toward the emission layer. The holes and electrons, which are carriers, are recombined in the emission layer to generate excitons, and then the excitons change from an excited state to a ground state, thereby generating light.
In this case, a transition into a ground state through a singlet excited state while emitting light, is referred to as “fluorescence”; and a transition into a ground state through a triplet excited state while emitting light, is referred to as “phosphorescence”. In the case of fluorescence, the probability of the singlet excited state is 25% and luminous efficiency of the fluorescence has a limitation. However, in the case of phosphorescence, because a 75% triplet excited state and a 25% single excite state are all used, theoretically, inner quantum efficiency may be increased up to 100%.
U.S. Pat. Nos. 6,596,415 and 6,465,115 disclose organic light-emitting diodes that use 4,4′-N,N′-dicarbazole-biphenyl (CBP) as a host for an emission layer. CBP is widely known as a host material for a phosphorescent emission material. A representative example of an organic light-emitting diode using phosphorescence is a green and red high-efficiency organic light-emitting diode that includes Ir(ppy)3 and PtOEP as dopants and CBP as a host to effectively emit light even in a triplet state (phosphorescence), wherein Ir(ppy)3 and PtOEP are phosphorescent pigments having a heavy atom that has a large spin-orbit bond, such as Ir or Pt in their centers. Recently, iridium (III) complex series are widely known as a phosphorescent emission dopant material, and (acac)Ir(btp)2, Ir(ppy)3 and Firpic are known as a red emission material, a green emission material, and a blue emission material, respectively. Also, an organic light-emitting diode that uses CBP as a host material for a phosphorescent emission material and BCP and BAlq for forming a hole blocking layer to obtain high efficiency, is disclosed, and also a high-performance organic light-emitting diode that uses a BAlq derivative as a host, is disclosed. However, these organic light-emitting diodes have a relatively short lifetime of 150 hours or less, and thus are not efficient for commercial use. A possible cause thereof is a relatively low glass transition temperature of 110° C. or less, high likelihood of crystallization, and low thermal stability of CBT. Due to these properties, CBP may deteriorate when deposited at high temperature.
Japanese Patent Application Publication No. 8-12600 discloses an organic light-emitting diode that uses a dimmer or terpolymer compound of phenylanthracene. However, because the organic light-emitting diode using the dimmer or terpolymer compound of phenylanthracene has two or three anthracenes, an energy gap is narrowed and color purity of blue emission decreases. Also, the compound is easily oxidized and thus impurities may be easily formed and thus, purification of the compound is difficult. To overcome these problems, an anthracene compound in which sites 1 and 9 are substituted with naphthalene or a diphenylanthracene compound in which an m-site of a phenyl group is substituted with an aryl group is used to manufacture an organic light-emitting diode. However, the organic light-emitting diodes using such compounds have low luminous efficiency.
Japanese Patent Application Publication No. 2000-3782 discloses an organic light-emitting diode that uses a monoanthracene derivative that is substituted with naphthalene. However, the organic light-emitting diode is not practically available due to its low luminous efficiency of about 1 cd/A.
U.S. Pat. No. 5,972,247 discloses an organic light-emitting diode that uses a phenyl anthracene structure. However, because the compound is substituted with an aryl group at its m-site, luminous efficiency of the compound is as low as about 2 cd/A, although its heat resistance is high.
Also, KR 2010-0090280 discloses an organic light-emitting diode in which an emission layer includes a fused aromatic cyclic compound that has anthracene and benzophenanthrene.